1. Field of the Invention
The present invention relates to a vehicle that utilizes electrical energy of a high voltage power source system, a power source system controller mounted on an apparatus that utilizes the electrical energy of the high voltage power source system, and a method of controlling a power source system. More specifically the invention pertains to a technique that utilizes a converter to convert the electrical energy of a high voltage battery into a low voltage and supply the converted low voltage and accordingly enables application of the electrical energy of a high voltage power source system including the high voltage battery.
2. Description of the Related Art
There are a diversity of recently proposed vehicles that utilize high voltage electrical energy of, for example, high voltage batteries. Typical examples of such vehicles include special vehicles that have a high voltage battery mounted thereon and carry out various works with the electric power of the high voltage battery, electric vehicles that run with the energy of a battery, and hybrid vehicles that have an internal combustion engine and a battery mounted thereon and use the power of the internal combustion engine in combination with the power of the battery. These vehicles generally have two batteries, that is, a high voltage battery that stores high voltage electrical energy used for driving and a low voltage battery that stores low voltage electrical energy used for controlling drives of the vehicle and regulating auxiliary machinery mounted on the vehicle. While the low voltage battery is used only as the auxiliary machinery battery in conventional vehicles driven with only the power of the internal combustion engine, the low voltage battery functions as the power source for controlling a high voltage power source system including the high voltage battery in addition to the function as the auxiliary machinery battery in these recently proposed vehicles. Namely the low voltage battery is of the greater importance with an increase of its loading. In order to ensure supply of electrical energy to the low voltage battery, the prior art electric vehicle has a converter circuit that converts the electrical energy of the high voltage power source system into a low voltage and charges the low voltage battery with the converted low voltage electrical energy.
In spite of such consideration, the voltage drop of the low voltage battery is inevitable, due to the continuously driven, large electric loading like headlights and the natural discharge from the battery in the inactive state over a long term. The proposed safety measures by taking into account the importance of the low voltage battery inhibit the system of the electric vehicle from being activated when the voltage of the low voltage battery is lower than a minimum reference voltage. While the voltage of the low voltage battery is lower than a predetermined level, the voltage of the power line for a controller that takes charge of control operations may fluctuated even with the use of a stabilizing power source unit. The prior art vehicle and the prior art power source controller mounted on an apparatus thus uniformly inhibit its activation when the voltage of the lower voltage battery is lower than the predetermined level.
The method of uniformly inhibiting the activation, however, undesirably lowers the convenience in use of the prior art vehicle and the prior art power source controller mounted on the apparatus. As mentioned above, the loading applied to the low voltage battery has been increasing significantly. A simple increase in storage capacity with the increasing load, however, has limitations, since it undesirably makes the low voltage battery bulky and heavy. The voltage of the low voltage battery that is subject to heavy loading may thus be deviated from a normal range and lowered to or below the minimum reference voltage. The prior art technique inhibits the power supply to the controller that takes charge of control operations relating to drives of the vehicle, thus prohibiting the vehicle from being activated. A simple decrease in minimum reference voltage undesirably lowers the safety factor of the whole system and is thus not adoptable.
The low voltage battery is also generally used as the power source for driving an apparatus that establishes the high voltage power source line, for example, a relay that connects the output of the high voltage battery with the power line of the high voltage power source system. The extreme drop in voltage of the low voltage battery makes the operations of such an apparatus unstable. Under the condition of the lowered voltage of the low voltage power source system, the contact of the relay that switches on and off the high voltage has weak working force. This may result in welding the contact. It is thus impractical to simply decrease the lower limit voltage of the low voltage battery that allows a start of the vehicle or the apparatus.
The object of the present invention is thus to provide a technique that brings out the best performance of a low voltage battery, while ensuring safety of a whole system. In the case of application to a vehicle, the technique allows a start of the vehicle while guaranteeing the normal operation of the whole system of the vehicle.
At least part of the above and the other related objects is attained by a vehicle that utilizes electrical energy of a high voltage power source system including a high voltage battery. The vehicle includes: a control unit that carries out controls related to driving of the vehicle; a low voltage power source circuit that supplies electrical energy of a low voltage power source system including a low voltage battery to the control unit; a battery voltage measurement unit that measures a voltage level of the low voltage battery; a converter unit that converts the electrical energy of the high voltage power source system into a low voltage and charges the low voltage battery with the converted low voltage electrical energy; and a recovery unit that, when the observed voltage of the low voltage battery is lower than a preset minimum reference voltage at the time of a requirement to start the vehicle, activates the converter unit to recover the voltage of the low voltage battery to the preset minimum reference voltage, prior to a permission to operate the control unit.
In the vehicle of the present invention, in response to a requirement to start the vehicle, the converter unit converts the voltage of the high voltage battery into a low voltage, charges the low voltage battery with the converted low voltage electrical energy, and thereby recovers the voltage of the low voltage battery to the preset minimum reference voltage, prior to a permission to operate the control unit. This arrangement ensures a start of the vehicle even when the voltage of the low voltage battery is in a specific range that is determined to be insufficient for starting the vehicle in the prior art arrangement.
A variety of configurations may be applicable for the connections among the high voltage battery, the converter unit, and the low voltage battery. In one preferable embodiment of the present invention, the vehicle further includes a connection unit that is actuated by part of the control unit with a power supply from the low voltage power source system and connects the high voltage battery with the high voltage power source system including the converter unit. This configuration enables the converter unit to be controlled together with the other devices of the high voltage power source system. In this configuration, one applicable structure may inhibit the operation of the recovery unit when the observed voltage of the low voltage battery is lower than an operation inhibiting reference voltage. Here the operation inhibiting reference voltage corresponds to a lower limit voltage that guarantees the normal operation of the connection unit. This arrangement effectively prevents the process for recovering the voltage of the low voltage battery from being carried out while the operation of the connection unit, which connects the high voltage battery with the high voltage power source system, is rather unstable. This accordingly further enhances the reliability of the vehicle.
Activation of the recovery unit represents the fact that the voltage of the low voltage battery once falls into the insufficient level to permit the operation of the control unit. It is accordingly preferable that the vehicle further includes an information unit that informs a driver of the activation of the recovery unit. The information unit informs the driver of the occurrence of the unexpected voltage drop of the low voltage battery and enables the driver to take some measures against the unexpected voltage drop of the low voltage battery, for example, charging the low voltage battery or inspecting the whole system.
In accordance with another preferable application of the present invention, the vehicle further includes a storage unit that registers the activation of the recovery unit in the form of a record and outputs the registered record in response to an external requirement. There are a variety of causes for the unexpected voltage drop of the low voltage battery that leads to activation of the recovery unit. Some causes are just transient due to erroneous operations like keeping the headlights on during a stop of the vehicle while other causes are more fundamental like deterioration of the low voltage battery. The measures suitable for the respective causes are required. The arrangement of registering the working record of the recovery unit enables the driver to presume the cause of the unexpected voltage drop by taking into account the frequency, the time, and the season of the occurrence and take appropriate measures.
The high voltage battery mounted on the vehicle may have a diversity of applications. For example, when the vehicle has a motor that outputs power required for driving the vehicle, the high voltage battery may be used as an energy source of driving the motor. The high voltage battery may be used as the power source of various power-driven apparatuses mounted on the vehicle.
In accordance with one preferable application of this embodiment, the vehicle may further includes: an engine that outputs power by means of combustion of a fuel; a generator that generates electric power with at least the output power of the engine; and a charging circuit that charges the high voltage battery with the electric power generated by the generator. Once the vehicle starts, the engine is driven to charge the high voltage battery. This arrangement enables the high voltage battery to be continuously kept in the sufficient state of charge once the vehicle starts, thereby keeping the low voltage battery in the sufficient state of charge.
The present invention is also directed to a power source system controller mounted on an apparatus that utilizes electrical energy of a high voltage power source system including a high voltage battery. The power source system controller includes: a low voltage power source circuit that supplies electrical energy of a low voltage power source system including a low voltage battery to a control unit that takes charge of controlling the apparatus; a battery voltage measurement unit that measures a voltage level of the low voltage battery; a converter unit that converts the electrical energy of the high voltage power source system into a low voltage and charges the low voltage battery with the converted low voltage electrical energy; and a recovery unit that, when the observed voltage of the low voltage battery is lower than a preset minimum reference voltage at the time of a requirement to start the apparatus, activates the converter unit to recover the voltage of the low voltage battery to the preset minimum reference voltage, prior to a permission to operate the control unit.
In the power source system controller of the present invention, when the voltage of the low voltage battery is lower than the preset minimum reference voltage at the time of a requirement to start the apparatus, the converter unit is activated to recover the voltage of the low voltage battery to the preset minimum reference voltage. This arrangement ensures a start of the apparatus even when the voltage of the low voltage battery is in a specific range that is determined to be insufficient for starting the apparatus in the prior art arrangement.
Any of the arrangements applied for the vehicle as discussed above may also be applicable for the power source system controller mounted on the apparatus. For example, the power source system controller may have an information unit that informs a user of the activation of the recovery unit.
There is a method of controlling the power source system, which corresponds to the power source system controller discussed above. The present invention is accordingly directed to a method of controlling a power source system in an apparatus that utilizes electrical energy of a high voltage power source system including a high voltage battery. The method includes the steps of: supplying electrical energy of a low voltage power source system including a low voltage battery to a control unit that takes charge of controlling the apparatus; in response to a decrease in observed voltage of the low voltage battery, converting the electrical energy of the high voltage power source system into a low voltage and charging the low voltage battery with the converted low voltage electrical energy; and when the observed voltage of the low voltage battery is lower than a preset minimum reference voltage at the time. of a requirement to start the apparatus, recovering the voltage of the low voltage battery to the preset minimum reference voltage, prior to a permission to operate the control unit.
In response to a requirement to start the apparatus, this method recovers the voltage of the low voltage battery to the preset minimum reference voltage. This arrangement ensures a start of the apparatus even when the voltage of the low voltage battery is in a specific range that is determined to be insufficient for starting the apparatus in the prior art arrangement.
The present invention is also directed to a method of controlling a start of a vehicle, which includes a converter that converts electrical energy of a high voltage battery into a low voltage and supplies the converted low voltage and utilizes electrical energy of a high voltage power source system including the high voltage battery. The method includes the steps of: in response to a requirement to start the vehicle, comparing an observed voltage of a low voltage battery with a preset minimum reference voltage required to establish a low voltage power source system including the low voltage battery; and when the observed voltage of the low voltage battery is lower than the preset minimum reference voltage, activating the converter to recover the voltage of the low voltage battery to the preset minimum reference voltage, prior to starting the vehicle.
Even when the voltage of the low voltage battery is lower than the preset minimum reference voltage at the time of a requirement to start the vehicle, this method activates the converter unit included in the vehicle to recover the voltage of the low voltage battery to the preset minimum reference voltage. This arrangement ensures a start of the apparatus even when the voltage of the low voltage battery is in a specific range that is determined to be insufficient for starting the vehicle in the prior art arrangement.
In accordance with one preferable application, the method of controlling a start of the vehicle may further include the steps of: setting in advance an operation inhibiting reference voltage, which is lower than the minimum reference voltage and represents a threshold value ensuring a normal operation of an apparatus that establishes a power source of the high voltage power source system; and when the observed voltage of the low voltage battery is lower than the operation inhibiting reference voltage at the time of the requirement to start the vehicle, inhibiting output from the high voltage battery to the high voltage power source system including the converter. This application clearly specifies the conditions for allowing the start of the vehicle and the conditions for inhibiting the start of the vehicle, based on the observed voltage of the low voltage battery, thus enabling the guaranteed safety to be compatible with the permission to start the vehicle.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.